Aaaw poor Perry.....he is gorgeous!
Something that might work for you, as it has for us, is to use the Science Selective Naturals Grain Free pellets.
We had one vet telling us that Guinea Pigs and Rabbits don't need pellets (even though they had Burgess ones for sale at the surgery?!), but our vet that we mostly see (at the same place) said that they are ok in moderation.
Thankfully we haven't had bladder problems with either Bubble or Squeak, but Squeak was overweight. Mid-December he weighed 1413g, and at the moment he is around the 1264g mark. This is since we switched to the grain free. Bubble did also lose a tiny bit of weight, even though he didn't need to, but not enough to cause concern.
They both love them, and from the start of introducing them over a 2 week period, they were eating these before their previous nuggets. We give them 12 each a day.....6 in the morning, and 6 in the evening.
Squeak especially is a bit of a nugget fiend, and so I would have felt bad stopping them altogether. We did try stopping for a few days, but Squeak was getting frantic looking for them, bless him.....especially as he can't see out of his right eye, and goes around in a circle to sort himself out to look for things.....with me being a softy, it was so sad watching him, and so had to go back to feeding them nuggets!